1. Field of the Invention
The present invention relates to a treatment method of semiconductor, a method for manufacturing MOS, and a MOS structure. In particular, the present invention relates to a method including a lateral etching step and a MOS structure so as to form a beak section in a recess in the MOS structure.
2. Description of the Prior Art
To increase the carrier mobility in the gate channel and decrease the resistance between the source and drain, in the semiconductor process a pair of recess are first formed at the both sides of the gate structure and a strained material such as C—Si and Si—Ge fills the recesses by a selective area epitaxial (SAE) so as to enhance the performance of the MOS.
However, before the strained material fills the recesses, a pre-cleaning step is usually performed on the surface of the substrate, especially on the surface of the recess, to facilitate the growth of the epitaxial afterwards. This so-called “pre-cleaning” usually includes treating the surface of the substrate with HCl gas under a low pressure. Because HCl gas would destroy the integrity of the surface of the substrate, a further vacuum treatment is carried out to treat the surface of the substrate to enhance the migration of Si to restore the integrity of the surface of the substrate. Finally, hydrogen gas is used to further treat the surface of the substrate to remove remaining chlorine and residues for the following epitaxial.
Because a layer of native oxide is spontaneously formed on the surface of the Si substrate once exposed to the air and the removal of the native oxide by the treatment of HCl gas is intrinsically ineffective and it takes so long to perform the vacuum treatment as well as to perform the HCl treatment, it is indeed necessary to provide a time-saving and more efficient method to treat the surface of the substrate. It would be even better if the stress of the gate channel is simultaneously enhanced.